1. FIELD OF THE INVENTION
This invention relates to the circulation of fluid between the surface of a subterranean well and the bore hole and more specifically relates to the simultaneous control of drilling fluid circulation or mud pumps and a choke communicating with the pump.
2. DESCRIPTION OF THE PRIOR ART
Conventional apparatus used in rotary drilling operations includes a drilling fluid circulation pump or mud pump used to circulate drilling fluids from the surface through the well bore. These fluids are used to remove cuttings made by a rotary drill. In normal drilling fluid or mud circulation, the drilling fluid is pumped down through the drill pipe, discharged through the bit and returns to the surface in the annular space outside the drill pipe and inside the drill hole and casing placed in the well. The rate of drilling fluid circulation is determined by the necessary upward flow velocity required for removing cavings and drill cuttings from the hole and by the jetting requirements of the bit. The inherent advantage of the rotary system of drilling is that a fluid is circulated for the purpose of removing drill cuttings and maintaining a hole in such condition that the drill string can be withdrawn readily and returned to the bottom whenever necessary.
During conventional drilling it is not uncommon to encounter a sudden pressure increase or kick caused by the release of downhole liquids or gases under pressure which can affect drilling fluid circulation. When a kick is encountered, it can be necessary to vary the rate at which drilling fluid is injected into the well or to change the weight of the drilling fluid. A choke, in communication with the pump, is used to prevent significant pressure changes in conjunction with a change in the speed of operation of the mud pumps. For example, a significant increase in downhole pressure occurring as a result of an increase in the drilling fluid circulation can conceivably fracture the producing formation causing serious damage.
In normal drilling operations, the mud pumps are controlled by the driller, using a driller's console located at the driller's station on a rig to monitor relevant drilling parameters, including the speed of the mud pumps. Furthermore, conventional well control circulation operations also require manipulation of the choke to regulate or control the fluid pressure, especially during changes in the speed of the mud pump. On a conventional drilling rig, the choke is normally controlled from a choke console, which can be positioned on the drilling floor, at a position remote from the normal location of a driller's console on a surface rig. Simultaneous control of both the mud pumps and the choke requires communication between the driller and one manning the choke console. Such communication is difficult, especially on engine driven drilling rigs. The noise and the use of different types of gauges on a rig cause confusion and makes such communication difficult, especially on engine driven drilling rigs. Furthermore, a more accurate gauge for pump strokes rate is conventionally located at the choke console, but conventional apparatus provide no means for using this more accurate gauge at the choke console to control the pumps. In a crisis situation, where the drilling crew is attempting to control the well, increased emphasis is placed on efficient communication and operation, which is difficult using prior art devices.